You can read this thread but the best way is to put her in an elevated cage or something with a wire bottom with food and drink. Do not give her anything that looks like a nest. It needs to be where it is predator safe. The idea is that if she cannot get to a nest and her bottom cools off she will break from being broody. Normally three days is enough but some can be more stubborn. If she goes back to the nest after three days, just do it again.
This is the method Old Hen was talking about. I’ve found it to be more effective than anything else and as Beginnergirl said, it is gentle.
Break a Broody Thread